The virtual machines in VMware Workstation use physical memory to run. With that being said, you can see that the amount of memory you have on your physical computer can be a limitation on how many concurrent virtual machines you can run at a single time. It can also be a limitation on running one virtual machine effectively. For example, if you have a Windows XP computer with 128 Mb of RAM, you won't be able to run VMware Workstation. If you had a Windows XP machine with 756 MB of RAM, you would be able to run one or two virtual machines maximum, but performance would be very slow. A computer with, say, 2 GB of RAM would allow you to run many virtual machines concurrently or one virtual machine with plenty of memory.

To make the most out of your memory, highlight the applicable virtual machine and edit the virtual machine settings. On the Hardware tab, highlight Memory and tweak this setting until you get the right amount of memory for your individual virtual machine. On a global level, you can configure memory by going to the Edit | Preferences | Memory tab (see Figure A). You have the following options:

Figure A

Reserved Memory

A Windows system doesn't do very well when you don't give it the memory it needs. When the operating system needs more memory, it begins to swap between memory and the page file. To prevent this, you can set the reserved memory accordingly. For example, if your host computer has roughly 1.5 GB of RAM and you always want to have 512 MB of RAM for your operating system, you would set the slider to roughly 841 MB.

How should the system allocate memory for virtual machines?

After specifying the reserved memory, you can choose one of the following options. Let's go over them in detail.

Fit all virtual machine memory in reserved host RAM. This setting gives you the best performance possible because it runs only the amount of memory you specify in the Reserved Memory box. For example, if you allocate 841 MB of RAM to reserved memory, your virtual machines will use only memory that is reserved. At this level, no swapping will take place. Now do you understand why this setting allows for great performance? If you have plenty of memory and are running only a few virtual machines, this setting is perfect for you. If your operating system is running only 256 MB of memory, this setting is less desirable because you will not have much memory to create virtual machines.

Allow some virtual machine memory to be swapped. This setting is great if you want to get more out of your memory. It allows some swapping to take place but gives you the benefit of having more virtual machines to work with. This setting can cause performance degradation, so monitor it until you find that spot where your operating systems are happy and the virtual machine performance is sufficient.

Allow most virtual machine memory. This setting allows you to swap as much host operating system memory as necessary. With this setting you can run many virtual machines, but you can hit a plateau and see a severe performance degradation.